Rotorspeed, you describe a scenario many of us will have experienced over the years. The London airspace and the ever taller 'encroachment of' buildings leave little room for error or malfunction in the reported weather conditions. Terms such as poor VMC, good VMC, VMC on top, decending through holes in cloud layers, are the unwritten lines in the regulations that corporate VFR helicopter pilots deal with most days in the UK to provide a viable service..